Fabie,
A very good point, but I think your conflating the issue. In fact, any two opposite gender roommates with separate bedrooms that do not engage in any kind of *conduct* can apply for a marriage license and receive all the benefits the State accords to such contractually committed couples. Separated opposite gender couples that live in separate homes but have not yet filed for divorce, and perhaps do not ever plan to (precisely because they may lose the legal benefits of marriage) can continue to claim the benefits of civil marriage under the law. Elderly couples that perhaps may not *act* can continue to claim the benefits of marriage.
It is clear that marriage under the law of the State is not contingent on marital *acts*; legally recognized marriage, and the benefits it provides arise from a simple contractual commitment between two people that gives rise to obligations to each other. In recognition of this commitment, the State considers the married couple to be more than just two individuals for a variety of purposes.
If civil marriage is not contingent on marital *conduct*, why – even according to we Torah-observant Jews that vilify the homosexual act – should the State be allowed to deny the benefits of marriage to any two individuals that are willing to take on the legal obligations that marital status imposes?
I think where we get really hung up is on the term used by the State to describe the legal status that gives rise to certain obligations and benefits – marriage. Perhaps if this civil institution were called something else – “interpersonal dependence,” for example – it would not bother us as much. We Jews consider marriage to be a special God-given concept heavily regulated by halachah, which makes it all the more precious. But let us not confuse nissuin with the “marriage” recognized by the State; the latter is simply a legal relationship, much like you business relationship to your partner in your LP or LLC.